This invention relates to deposition of barrier films for inhibiting penetration by oxygen or other gases employing a cross-linked acrylate layer and a layer of oxygen barrier material.
Many products, including many food products, are packaged in thin plastic sheet bags or the like. The thin films are desirably resistant to permeation by oxygen, water vapor and odorous gases. This can, for example, be important for protecting a food from environmental gases and also for retaining the aroma of food as it is stored.
Such barrier films are commonly made of costly plastics because less costly films are too permeable to oxygen or water to give a long shelf life. Reduced cost barrier films are highly desirable.
There are many products that are packaged in plastic bottles, tubes or vials which also need protection from oxidation or contamination by environmental gasses or which must be in impermeable containers so that components of the contents are not lost by diffusion through the containers. An example comprises medical products which may presently be enclosed in glass bottles because plastics are not suitable. It would be desirable to make such containers of plastic material which is physiologically acceptable, however, such materials may also be sufficiently permeable to oxygen that they are unsuitable for medical products. Food packages are also desirably packaged in plastic, but shelf life may be compromised by permeability. It is, therefore, desirable to provide a coating on such vessels for these critical applications.
There is, therefore, provided in practice of this invention a barrier with low oxygen and water permeability having a thermoplastic substrate, a cross-linked acrylate layer on one face of the substrate and a layer of oxygen barrier material deposited on the same face of the substrate as the acrylate layer, preferably over the acrylate layer, or in some embodiments, under the acrylate layer. In one embodiment, the acrylate layer is a polymerization product of an acrylate monomer having a molecular weight in the range of from 150 to 600. Alternatively, the acrylate layer may be formed from a photopolymerizable acrylate that is sufficiently low viscosity to be sprayed on the substrate or applied by dipping. Preferably, there is another cross-linked acrylate layer over the oxygen barrier layer. It is preferable to deposit a top acrylate layer over a metallized layer before the metallized layer contacts any surfaces.
The surface of the thermoplastic substrate is prepared for deposition of the acrylate by either heating the surface of the substrate above its melting point without deforming the substrate or by plasma treating the surface for enhancing adhesion of the acrylate. Chilling the substrate enhances deposition efficiency.